It has heretofore been proposed to provide a one-piece dual-chamber container by molding, such as by extrusion blow molding, separate container sections and then securing the sections to each other to form a unitary container. U.S. Pat. No. 5,823,391 is exemplary of this technology. It has also been proposed to form an extrusion blow-molded dual-chamber container by extruding a single tube, placing the tube in a blow mold with dividing wall portions that pinch the tube diametrically, and then blow molding the tube halves to the interior confines of the respective mold cavities. U.S. Pat. No. 5,882,574 illustrates technology of this character.
It has also been proposed to form hollow plastic containers by an injection blow molding (IBM) process. In such a process, a preform is injected into a first mold cavity around a core rod, and the core rod and preform are then moved to a second mold cavity. The preform is blown to the interior confines of the second mold cavity by air injected through the core rod, and the container is then removed from the core rod and the second mold cavity. U.S. Pat. No. 3,707,591 illustrates a turret-type machine for automated manufacture of hollow plastic containers in an injection blow molding operation.
Among the objects of the present invention are to provide a method an apparatus for injection blow molding a dual-chamber container as an integral unit so as to eliminate any requirement for attachment of separate container sections by gluing, welding, base cups or a dual closure in a post-molding operation, that have the potential for providing a two-color container, that exhibit enhanced neck finish dimensional stability, and/or in which the containers are finished upon ejection from the blow mold, which is to say that the containers do not require post-mold trimming of moils, tails or other process scrap. Another object of the present invention is to provide a dual-chamber IBM container made by such a process and/or such an apparatus.
A method of forming a dual-chamber container in accordance with a presently preferred embodiment of the invention includes providing a blow mold having a pair of adjoining cavities that are open to each other. A pair of mold preforms are constructed having non-uniform wall thicknesses, preferably by injection molding the preforms around associated core rods. The preforms are then non-centrally positioned in respective mold cavities such that a portion of each preform of greater wall thickness is spaced a greater distance from the opposing wall of the associated cavity than the portion of each preform of lesser wall thickness. The preforms are then blow molded simultaneously against the cavity walls and against each other so that the preforms are contact-welded to each other to form an integrally molded dual-chamber container of substantially uniform wall thickness. In the preferred embodiment of the invention, mold wall portions partially divide the blow-mold cavities from each other, and the preforms are placed in the blow-mold cavities such that the preforms are closer to the portions of the cavities that open to each other than to opposite walls of the cavities.
An apparatus for injection blow molding a dual-chamber container in accordance with a presently preferred embodiment of the invention comprises a pair of core rods carried on a transfer head. Means including the transfer head simultaneously position the core rods in first mold cavities for injection molding a preform around each core rod, with the injection mold cavities being constructed such that the preforms have non-uniform wall thickness around the core rods. Means including the transfer head then position the core rods and the preforms in a pair of second mold cavities that are open to each other along a common wall portion, with the preforms being non-centrally positioned in the second cavities such that a portion of each preform of greater wall thickness is spaced a greater distance from the opposing wall of the associated cavity than the portion of each preform of lesser wall thickness. The preforms are then blow molded within the second mold cavities such that adjacent portions of the preforms are contact welded to each other at the common wall portion of the cavities and the container has substantially uniform wall thickness.
A dual-chamber container in accordance with a third aspect of the present invention thus includes an integrally molded one-piece body having first and second blow molded chambers separated from each other by a common dividing wall contiguous with both of the chambers—i.e., forming a wall section of each chamber. The container also includes first and second injection molded finishes forming outlets for the respective chambers. The chambers each have a width parallel to the common wall, and the common wall occupies less than the entire width of the chambers. The chambers have separate walls contiguous with the common wall for the remainder of the width of each chamber. The dual-chamber container has substantially uniform wall thickness, and is formed by simultaneously blow molding a pair of preforms having non-uniform wall thicknesses while the preforms are non-centrally positioned in a pair of mold cavities. A portion of each preform of greater wall thickness is spaced a greater distance from the wall of the associated cavity than is a portion of each preform of lesser wall thickness. The preforms are blown against each other and contact welded along the common wall that divides the chambers.